This invention relates generally to the field of a metallurgical apparatus and particularly to remotely controlled devices and methods for cutting a pipe from within. More particularly, the invention relates to the manner in which a cutting device is mounted in the pipe and deployed to the point where the cut will be made.
The invention originated in the field of nuclear reactor dismantlement operations where physical access limitations necessitated that certain pipe cuts be made from inside the pipe at some distance from the end of the pipe and be made under remote control.
The inventive device was conceived to allow thick-walled reactor vessel main coolant loop piping to be reliably severed from the reactor vessel where conditions prevented access to the outside of the pipe. It was necessary to sever a pipe from the reactor vessel approximately at the juncture of the reactor vessel and the pipe. Access to the outside of the pipe was only available several feet from the desired cut line at the vessel-pipe juncture. It was also necessary to utilize a cutting process which could reliably sever a pipe up to about 4.5 inches in wall thickness. No existing system or equipment could be found which performed this task.
Development of the device required several plasma arc torch (PAC) process adaptations. It was also necessary to devise ways for routing PAC services to the torch while providing necessary control features compatible with the geometry of the piping, the rotating and translating motions of the device, and the available space within the pipe. In addition, the device needed to be capable of surviving the high temperature environment of the PAC process, including the molten by-product (dross) from the cutting.
Although numerous forms of pipe cutting devices exist in the art, some examples of which are listed below, none has been found which performs the required function of cutting large pipes at inaccessible locations under remote control.
U.S. Pat. No. 3,711,076 to Goetz (1973) discloses the use of an oxyacetylene torch attached to the distal end of a radial arm rotatably mounted on a frame within a large pipe. The frame comprises expandable radial arms for locating the frame within the pipe and a drive mechanism for rotating the radial arm. No provision is made for remotely controlling the location of the torch.
U.S. Pat. No. 4,455,015 to Larikka (1984) discloses a steering apparatus for an autogenous cutting torch for cutting holes of desired shape in flat or curved sheet walls. The apparatus provides for guiding a cutting torch along a preset path with a reciprocating or oscillating motion provided by cams or cranks. No provisions are made for severing pipes or remotely controlling the location of the torch.
U.S. Pat. No. 4,524,511 to Montiero (1985) discloses the use of cutting blades attached to pivoting arms mounted on a rotating axial drive shaft within the pipe. The shaft is supported by a centering device located at the open end of the pipe and driven by an external power source. No provisions are made for remotely controlling the location of the cutters.
U.S. Pat. No. 4,986,314 to Himmler (1991) discloses the use of a wheel-mounted carriage for traveling within a pipe. The carriage comprises a working head mounted on one face of the carriage and rotatable around a longitudinal axis of the carriage. The head can be used to mount various cutting and machining tools. The carriage and its tools are driven by hydraulic motors and its operation can be monitored by an on-board TV camera. This device is designed for use primarily in repairing pipelines and is substantially more complex and expensive than required for the present application.
U.S. Pat. No. 5,006,687 to Fujita, et al. (1985) discloses methods for cutting steel pipe pilings from within using either a non-contact process such as a plasma arc torch or a contact process such as a cutting grinder, or both. One method includes the use of a drive mechanism suspended by ropes from the top of a vertical pipe. The drive mechanism is centered within the pipe by expandable am is after arriving at the desired vertical position. The cutter is rotated circumferentially inside the pipe by the drive mechanism. In another method, the cutter is suspended on a rod hanging in pendulum fashion from a pivot in a disk on the upper end of a vertical pipe. The cutter in this case is rotated from the upper end of the rod and located radially by tilting means at the top, or guides at the bottom, of the rod. The methods do not provide for three-axis location control of the cutter while in operation.
U.S. Pat. No. 5,368,423 to Hanna (1994) discloses a skid-mounted robotic cutter for re-establishing lateral connections in a lined sewer pipe. The cutter comprises a motor driven cutting tool oriented for cutting through the inserted lining of a main pipe where the lining covers the opening into a lateral pipe at its junction with the main pipe. The robotic cutter does not provide for severing the main pipe in which it is located.
U.S. Pat. No. 5,685,078 to Obst and Gray (1997) discloses a device comprising an annular cutter head driven by shaft from the open end of the pipe. The cutter head comprises a plurality of cutter wheels located in radial slots around the periphery of the head. As the cutter head is driven by the shaft, the cutter wheels are expanded radially by a conical member located axially within the annular cutter head. No provision is made for remote control of the cutter while in operation.
U.S. Pat. No. 5,815,926 to Ekern (1998) discloses a hand held device comprising a shaft having an upper end adapted for connection to a rotational power tool and a lower end to which a rotary cutting blade can be attached. A sleeve surrounding the shaft encloses a collar which can be clamped to the shaft to locate the sleeve axially on the shaft while permitting the shaft to rotate freely within the sleeve. The sleeve has a disk located on its end adjacent to the cutting blade. In operation, the cutting blade can be inserted into the open end of a pipe to a distance determined by the location of the disk and the pipe cut by manually moving the rotating cutter blade around the internal periphery of the pipe. This device provides a very simple illustration of internal pipe cutting at an externally inaccessible location; of course, it does not have the required capability of cutting large pipes or of remotely controlled operation.
None of these prior art devices performs the required function of cutting large pipes at inaccessible locations under remote control.
The invention is a remotely controlled internal pipe cutting device primarily used for cutting pipes in any orientation (i.e., the pipe is horizontal, vertical or inclined), where the outside of the pipe is inaccessible at the line where the cut is to be made. The device is useful where the pipe has a straight section extending to an accessible open end located a distance of up to several pipe diameters from the desired cut line. The device comprises an axial ram within a rotational cylinder which is enclosed in a housing attached at a proximal end to a support bracket. A radially movable cutter, preferably a plasma arc cutting (PAC) torch, is attached to the distal end of the ram. A drive mechanism, containing motors and mechanical hardware for operating the ram and cylinder, is attached to the proximal end of the housing. To use the device, the distal ends of the ram, cylinder and housing are inserted into the open end of the pipe and the support bracket is attached to the end of the pipe, thereby supporting the device in cantilever fashion within the pipe. In operation, the ram and cylinder provide for the movement of the cutter axially and circumferentially, and an arm and cable assembly attached to a remote motor provide for the movement of the cutter radially, within the pipe. The control system can adjust feed and rotation speeds manually and be operated remotely to control the position and movement of the cutter to obtain the desired cut.
A schematic which illustrates the device in its environment is shown in FIG. 1. A pipe 3 to be severed from a reactor vessel 4 extends from the vessel through a wall 5. The wall prevents access to the pipe at its juncture with the vessel. The pipe cutting device comprises an internal device 1 and an external device 2. The internal device 1 is attached to the accessible end of pipe 3 and cantilevered within the pipe. A PAC torch 11 is thereby located within the pipe and can be translated to the desired cut line and rotated to perform the cut. The external device 2 contains the drive mechanism, along with other external equipment, and provides the driving functions and services for the internal device 1.
The internal device is mounted onto the pipe end by a support bracket which supports the internal device within the pipe in a cantilever fashion. An axial ram provides translational (longitudinal to the pipe) motion for the torch assembly, which is mounted on the distal end of the ram. The translational motion of the ram is controlled by an electric motor and associated gear train ball screw assembly, and a motor controller. Rotation of the ram, which allows the torch to move around the inside periphery of the pipe, is provided by a rotation cylinder, associated gear train, and another motor and associated controller. The translational and rotational positions of the torch are determined by feedback from position encoders attached to the associated gear trains.
Radial motion of the torch assembly is controlled by a cable and reel assembly attached to a motor and controller which automatically adjusts the separation between the torch tip and the wall of the pipe to maintain the proper voltage across the arc when a PAC torch is used.
The device allows longitudinal cuts to be made to reach the circumferential cut area. This allows the piercing limitations of plasma arc cutting to be utilized in the thinner cut region.
The device preferably utilizes a commercially-available plasma arc cutting (PAC) process, with a specially designed plasma arc cutting torch, attached to an internal device which operates within the pipe and an external device which provides the drive mechanism and controls and services for operating the cutting device. This device can be used to reliably sever a pipe up to about 4.5 inches in wall thickness. This device permits a four-inch-thick pipe wall to be cut at a rate of 10 inches per minute.
The internal and external devices can be adapted for use with other cutting processes such as abrasive waterjet cutting. Use of the PAC or abrasive water jet processes allows cutting of pipes made of materials other than carbon steel, such as corrosion resistant steel (CRES) or CRES-clad.
Direct access to the reactor vessel piping is only available several feet from the desired cut line on the reactor vessel piping. Therefore, it is necessary to cut and remove a section of the pipe at this remote location and use the cut end of the pipe to mount the internal cutting device. The device is cantilever-mounted on the pipe end and extends through the pipe, toward the reactor vessel, to the desired cut location. An advantage of this is that it does not require contact with the inner surface of the pipe and therefore the process is not affected by surface irregularities such as weld reinforcement.
The invention effectively cuts using nitrogen and oxygen as the cover and cooling gasses in the PAC process without the use of potentially explosive hydrogen gas.